Why doesn't CRM CreatedOn field appear as a source field?

I am trying to map data from a Microsoft CRM database into a SQL Server. I am trying to copy the InvoiceBase table and one of the fields I want to copy is the CreatedOn field. However it does not appear as a field I can copy in Scribe. I then added InvoiceDetailBase as a ChildDataObject and then specifically added it's CreatedOn field to my list of fields under the fields tab, but still it did not appear as a source field. Why doesn't CreatedOn appear? I see plenty of other date fields, it is just CreatedOn that does not appear as a source field. Any help with this would be greatly appreciated! Thank you!

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